Communication networks support the exchange of messages between communication devices. Communication protocols, sometimes called standards, have been established to govern the operation of each type of communication device on a communication network. Each communication protocol, however, may not be interoperable with every other communication protocol. As such, a first communication device using a first protocol on a first communication network may not be capable of exchanging messages with a second communication device using a second protocol on a second communication network.
Traditional Communication Systems
Communication devices involved with a telecommunication session are referred to as a caller device and a recipient device. The subscriber, or user, of the caller device, typically enters an identifying number of the recipient device into the caller device. The communication network supporting the operation of the caller device receives the identifying number from the caller device and performs an initialization procedure to establish a connection between the caller device and the recipient device. The network supporting the operation of the recipient device is contacted to determine if the recipient device is available to establish the communication session. If available, an open switched connection is traditionally established between the caller device and the recipient device through their respective communication networks.
Packet-based Communication Systems
In Internet Protocol (IP) networks, the communication process is very different from prior conventional telecommunication systems. In an IP network communication, there is no open switched connection established between the caller and recipient devices. The information being transmitted between the caller and recipient devices is broken into packets of data, and each packet of data is transmitted to the recipient device in pieces. The data packets individually contain routing information to direct each packet to the recipient device. These packets are then reassembled into a coherent stream of data at the recipient device.
An IP standard protocol supports digital communication over the Internet between devices located on different networks. The IP standard protocol also specifies the requirements of system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in the communication system. A transmission protocol, called the Transmission Control Protocol (TCP), provides connection-oriented, end-to-end data transmission between packet-switched computer networks. The combination of TCP with IP (CP/IP) defines the protocols necessary for data transfer and communication between computers on the Internet. The TCP/IP standard is used in most packet switching networks that are coupled across a computer network boundary. The TCP/IP protocol also defines how IP-based data packets should be processed, transmitted, and received on the Internet.
IP and TCP Protocols
A generalized information packet used in an IP-based communication is shown in FIG. 1. The information packet is in Type-Length-Data (LTD) format. As shown in FIG. 1, the Type 110 variable (designated by “T”) occupies the first 8 bits of the general extension, the Length 120 variable (designated by “L”) occupies the next 8 bits of the general extension, and the Data 130 variable (designated by “D”) occupies the remaining bits in the general extension based upon the data content (type and length). The Type 110 variable indicates the particular type of data packet found therein, and the Length 120 indicates the length in bytes of the data field within the extension. The Data field 130 may be zero or more bytes in length, and includes the data that is being transmitted.
Specialized Mobile Radio Systems
Specialized Mobile Radio (SMR) systems are traditional analog radio systems used for dispatch services. Dispatch services usually require communication with mobile vehicles or users, such as taxicabs, construction vehicles, freight deliverylpickup vehicles, and couriers. Generally, these systems permit voice communication between two or more mobile radio transceivers.
A typical form of communication over these radio systems is a one-way, or simplex, message transmission. In the simplex transmission, the first subscriber actuates the transmit button on a first transceiver (mobile unit) to transmit a message, and then the subscriber releases the transmit button on the first transceiver after completing the transmission. After releasing the transmit button on the first transceiver, the second subscriber can respond to the first subscriber by actuating the transmit button on a second transceiver to send a response message.
Enhanced Specialized Mobile Radio (ESMR) systems utilize digital technology for communications. This newer digital SMR technology supports additional features and services such as paging, inventory control, vehicle location, credit card authorization, database access, and voicemail. ESMR systems are low power output systems capable of covering a radius of between two to eight miles. SMR systems, in contrast, are higher power output systems that can cover a radius of up to about 30 miles.
Wireless Communication Systems
A typical cellular communication system is comprised of multiple cell sites covering an intended geographic service region. Referring to FIG. 3, each cell site 301, 302, 303, and 304 supports wireless communication within its service area represented by a hexagon. Each cell site 301, 302, 303, and 304 can cover an area comparable to the radius of a transmitter on an ESMR digital communication system.
Cell site 301 supports wireless communication with a mobile unit or mobile station (MS) 305. The cell site 301 supports communications to MS 305 by using at least one antenna 310 connected by communication link 311 to a base station transceiver substation (BTS1) 315. The MS 305 can include different communication devices capable of wireless communication, such as a cellular phone, a computer with a transceiver attached to the modem, a pager, or a two-way radio.
The BTS1 315 is attached to a base station controller (BSC) 350 via communication link 332. The BSC 350 will control communications on a number of different cell sites, such as cell sites 302, 303 or 304. BSC 350 is connected to a cell site 302 and BTS2 318 via communication link 331. BTS2318 is connected to antenna 323 via communication link 314. BSC 350 is connected to cell site 303 and BTS3 317 by communication link 333. BTS3 317 is connected to antenna 322 by communication link 313. BTS4 316 and cell site 304 are connected to BSC 350 by communication link 334. BTS4 316 is also connected to transmission antenna 321 by communication link 312.
Because of similarities in system requirements, an ESMR system can also be supported on a conventional cellular system described in FIG. 3. The combination of a cellular and ESMR system dramatically increases the transmission capacity of a dispatch communication system over the older SMR analog system. For example, a subscriber in a dispatch service using the cellular ESMR technology can send and receive data, alphanumeric messages, and even make regular cellular telephone calls using the same mobile unit that provides radio contact with the base station and his dispatcher/controller. As such, a cellular ESMR system expands the capabilities and functionality of dispatch communications over the analog SMR communication systems.
The Evolution of Hand-held Devices
Various communication devices are available on the market that support many functions found on phones, pagers, and computers. Lately, market forces have forced the integration of computer technology, Internet Protocols (IP), and digital packet data transmissions onto single-unit, multiple purpose hand-held devices. For instance, many cellular phones are now capable of accessing the Internet, displaying data, processing data, and transmitting alphanumeric messages. Similarly, other single-unit hand-held devices have incorporated the capability of accessing the Internet, transmitting text messages, and processing cellular communications.
A hand-held device uses an operating system program to control its operation. One programming language recently adopted by many handheld devices manufacturers for an operating system is the JAVA™ programming language. JAVA™ supports the execution of many types of programs operating on a variety of computing devices. Because of the limited memory requirements of specific variants of JAVA™, computer software programmed in the JAVA™ language can be operated on limited-memory hand-held devices and other electronic equipment.
A variant of the basic JAVA™ programming environment is the JAVA 2 Micro Edition™ (JAVA 2 ME) which may use K-Virtual Machine (KVM) technology. The JAVA™ KVM programming environment is highly optimized for use in limited-memory devices with approximately 128K of available memory. The JAVA™ KVM programming environment can be used on devices containing 16-bit or 32 bit processors and a total memory of approximately 256K. Computer programs and applications using this technology can be found in cellular phones, pagers, and other hand-held communication devices.
Non-compatible Networks, Protocols, and Standards
Presently, different communication networks (e.g. cellular and ESMR networks) utilize different, non-compatible protocols to support communications on a system. Different types of protocols could include wireless Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Global Systems for Mobile Communications (GSM), and Enhanced Specialized Mobile Radio (ESMR) systems.
In an ESMR communication system, a specialized protocol is used that allows subscribers to transmit messages to another subscriber or group of subscribers one-at-a-time in a simplex mode. Cellular systems do not normally use the same communication protocol to transmit communications as an ESMR system, and therefore, traditional cellular systems do not support simplex communications. To support the ESMR function on a cellular network, two separate and distinct communication protocols must be supported on a single hand-held device and its associated communication networks. The real challenge of supporting ESMR simplex communications on a cellular communication network is the integration of two separate system protocols onto a single communication device and network.